This project is an attempt to determine whether glycine is utilized as a neurotransmitter by the identified neurons R3-R14 in the parietovisceral ganglion of the marine gastropod Aplysia californica. This is to be accomplished by (1) locating the terminals of the major axons of R3-R14, (2) characterizing the metabolism of glycine in R3-R14, (3) characterizing the interactions of R3-R14 with their targets, (4) characterizing the subcellular localization of glycine in R3-R14, (5) determining the effects of glycine on the targets of R3-R14, and (6) determining whether glycine is released in conjunction with electrical activity in R3-R14. R3-R14 are unique among Aplysia neurons examined in containing high glycine concentrations and in possessing a specific glycine uptake system. In the past year we have described the terminals of R3-R14, characterized axonal transport of glycine in R3-R14, and shown that in the axon glycine is associated with the characteristic vesicles present in R3-R14. These observations are the most clearcut demonstration to date of the axonal transport of a free amino acid, which is currently an issue of some controversy. Also, this is the first demonstration of an association of amino acids putative neurotransmitter with storage vesicles in a neuron.